Answer:
The unification campaign of Prithivi Narayan Sah proceeded towards the east after Kathmandu Valley because of the following reasons.
1) Because there were many places where people belonging to Nepali ethnicity and languages residing in the eastern regions (Sikkim, Darjeeling, Assam, Bhutan, Burma etc.)
2) Trade route to Sikkim, India, Bhutan and Tibet was possible from eastern regions.
3) To stop the East India company from marching ahead into Nepal territory in the far eastern borders.
4) There were too many smaller kingdoms in the eastern regions which could be easily captivated as there was no unification among the smaller kingdoms and they could be attacked easily.
